1. Field of the Invention
This invention relates to inflatable structures for use in medicine and other applications, and methods of manufacture and use of the same.
2. Description of the Related Art
Inflatable structures, such as balloons, are widely used in medical procedures. A balloon is inserted, typically on the end of a catheter, until the balloon reaches the area of interest. Adding pressure to the balloon causes the balloon to inflate. In one variation of use, the balloon creates a space inside the body when the balloon inflates.
Balloons may be used to move plaque away from the center of a vascular lumen toward the vasculature walls, such as during an angioplasty or a peripheral vasculature procedure. During this procedure, a balloon tipped catheter is placed in a vascular obstruction. As the balloon is inflated, the vessel constriction is dilated, resulting in improved blood flow.
Optionally, the balloon may have a stent placed over it. The balloon expands the stent in order to create a scaffold structure that keeps the vessel from constricting after the balloon is removed. Stents are used throughout the body, including the coronaries, other portions of the vasculature, the GI tract, the biliary ducts and the urinary and gynecologic tracts.
High pressure balloons may be used to expand constrictions in bone, such as in the sinuses in sinuplasty.
Balloons may be designed to make space in bone. After an osteoporotic compression or trauma-induced fracture in a vertebral body, a balloon can be inserted into the vertebral body through a working channel such as a cannula. The balloon is then inflated, creating a void in the bone. The balloon is withdrawn and bone cement is injected to internally stabilize the fracture. This procedure may be referred to as Kyphoplasty.
Sometimes the vasculature has a narrowing that is calcified, which can create a particularly difficult obstruction for dilation. As the vessel is increasingly narrowed, it can become what is known as a CTO (Chronic Total Occlusion). CTOs can be difficult to pass through with a device such as a guidewire or catheter and can be difficult to dilate or open. The balloon used to open a CTO is ideally resistant to puncture and operates at a very high pressure.
Balloons can have structures attached to their surface. These structures can include blades or stiffening rods. These structures may slice a vessel open. These structures may apply pressure to the inside of a vessel in order to expand the vessel.
Balloons can be used to locally deliver captured volumes of a radioactive substance. The procedure may be known as brachytherapy.
Balloons can be used to intentionally obstruct vessels. Stenting of the carotids serves to treat atherosclerotic carotid vessels. Stenting of the carotids may be less invasive than an endarterectomy. Stenting of the carotids may release a stream of debris that can travel to the brain, causing strokes. Expanding a balloon in the carotid artery above the area of treatment can prevent this debris movement to the brain, thereby reducing the potential for adverse complications.
Balloons may be used to position and deploy arterial grafts that repair aneurysms.
A balloon may deliver targeted drugs in the body by isolating a space for treatment.
A balloon may deliver targeted drugs in the body by having many tiny holes in the balloon wall. The holes in the balloon wall may allow the drug to slowly flow into the area surrounding the balloon.
Balloons may be used endoscopically to open up constrictions in the body, such as those in the esophageal tract, the urological tract, the biliary tract, the fallopian tubes, the carpal tunnel or esophagus, or other portions of the GI tract (the alimentary canal). A balloon may be used to expand constrictions in the urethra, including for Benign Prostate Hyperplasia (BPH).
Balloons may be used in the heart valves, including during Percutaneous Transvenous Mitral Valvuloplasty (PTMV) or Percutaneous Transvenous Mitral Balloon Commissurotomy (PTMC) or Mitral Annuloplasty. The balloons can be utilized to expand stenosed or calcifically-narrowed structures. The balloons can be utilized to expand valves to a tissue-opposed diameter.
A balloon may be used to affix a device inside the body. Another device may then use the balloon as a structure that the device can react against. The device may use this reaction force to move in the body. A balloon and a device may be used in the GI tract. A balloon and a device may be used during a Double Balloon Enteroscopy procedure, or during colonoscopy.
Balloons may be used to create space in the body or to move organs in body. Balloons can be used to manipulate organs along tissue planes.
The balloon may locate a cutting instrument in some ablative procedures. The balloon may position a diagnostic device.
An inflatable structure can be used to open space in tissue or to pull sclerotic structures apart, or to advance structures introduced herewithin to the body.
A balloon may be used to occupy a volumetric space for long periods of time, such as a device used to impart satiety at lower food volumes, as in Bariatric procedures.
A balloon can be used to create captured volumes that serve to transfer heat or cold. A balloon can provide small crossing profiles that then expand locally to create large volumes with high surface areas and intimate tissue contact. This is utilized in the prostate to treat BPH.
Balloons can be used as implants, creating an anatomical conforming structure advantageous to improved local fit.
Balloons have been suggested which seal against a lumen wall, then continue to dynamically seal as they are manipulated backwards or forwards. These balloons may be used in the GI tract. These balloons may be advanced forward or backward by pressure gradients on either side of the balloon.
Balloons may be used as pressure cuffs, such as those found in Lap-Band bariatric devices. By changing the pressure in the balloon, the inner diameter can grow or shrink. Changing the diameter alters clinical results.
Balloons may be elongated and used for movement through long lumens, including the GI tract.
Inflatable structures can be made into everting tubes, which have been utilized in gynecologic and urinary procedures, and have been suggested for GI procedures.
Two basic types of balloons are utilized: One is a high pressure, low-compliance balloon. The other is a lower pressure, high-compliance balloon.
High-compliance medical balloons are often composed of urethane, latex, silicone, PVC, Pebax, and other elastomers. As the pressure in a high-compliant balloon is increased, the balloon dimensions expand. Once the pressure is reduced, the high-compliance medical balloon may return to its original shape, or near its original shape. High-compliance medical balloons can easily expand several times in volume between zero inflation pressure and burst.
Traditional high-compliance medical balloons can be inadequate for many reasons. High-compliance, or highly elastic medical balloons typically cannot reach high pressures because their walls have a low tensile strength and their walls thin out as the balloon expands. In some instances, high-compliance medical balloons provide insufficient force to complete a procedure. Exceeding the rated pressure of a high-compliance medical balloon creates an excessive risk of balloon failure which can lead to serious complications for the patient.
High-compliance medical balloons also have poor shape control. As a high-compliance medical balloon expands, it may assume a shape dictated mostly by the particulars of the environment inside the patient rather than the clinical goals. In some cases, this can be contrary to what the medical practitioner desires. Many medical procedures are predicated on forming a particular balloon shape reliably.
High-compliance medical balloons often suffer from poor puncture resistance.
It is generally desirable that the medical balloon be able to enter and exit the body with as little trauma as possible. Therefore, a small deflated balloon profile is an important consideration in balloon design. This requirement favors materials with high strength to volume ratios. High-compliance medical balloons do not use materials that have outstanding strength to volume ratios.
In some cases, it is desirable that the medical balloon have a strong chemical resistance. For instance, a principal component of bone cement is methyl methacrylate, which readily degrades some elastomers, such as urethane. Therefore, many high-compliance medical balloons are not compatible with the introduction of aspects of the procedure that the high-compliance medical balloon is meant to support.
Low-compliance, high pressure medical balloons substantially retain their shape under comparatively high pressures. PET (polyethylene terephthalate) is the most common material for use in high pressure low-compliance balloons. PET is commonly used for high-performance angioplasty balloons. PET is stronger than other polymers, can be molded into a variety of shapes and can be made very thin (e.g., 5 μm to 50 μm (0.0002 in. to 0.002 in.)), thus giving these balloons a low profile.
Balloons made from PET walls are fragile and prone to tears. When pressed against a hard or sharp surface in the body, such as bone, PET balloons have poor puncture resistance. PET is very stiff so balloons made from PET may be difficult to pack or fold into a small diameter or with good trackability (i.e., the ability to slide and bend over a guidewire deployed through a tortuous vessel). In some applications, PET's chemical resistance can lead to unwanted adhesion, degradation or destruction of a PET balloon during a procedure.
Balloons made from PET, while stronger than most other balloons made from homogenous polymers, may still not be strong enough to hold pressures sufficient to complete certain medical procedures.
The PET in a balloon wall may be oriented during manufacture. However, the oriented PET may not have strength in all directions exactly proportionate to the expected load.
PET, like most low compliance balloons, is usually blow-molded. The blow molding process makes it difficult or impossible to create certain shapes. Blow molding can result in wall thicknesses in the balloon that do not match the material thicknesses to the expected load.
Nylon balloons are an alternative material for low-compliance, high pressure balloons. These balloons are typically weaker than PET balloons and so can contain less pressure. Nylon readily absorbs water, which can have an adverse affect on Nylon's material properties in some circumstances. Nylon has improved puncture resistance over PET and is more flexible than PET.
Low compliance fiber reinforced medical balloons have recently become commercially available for peripheral vascular procedures. High strength inelastic fibers are used as part of the low compliance fiber reinforced medical balloons to strengthen the walls of the balloon while further lowering strain rates. High strength inelastic fibers such as Kevlar, Vectran, Dyneema and carbon fiber all have strength to volume ratios that greatly exceed that of PET or Nylon. The high strength inelastic fibers are combined with a flexible adhesive and, optionally, one or more polymer walls to form a balloon.
Low compliance fiber reinforced medical balloons may suffer from several problems. These balloons may have a low volume ratio of high strength inelastic fiber to the total material volume in the balloon walls. It is reasonable to assume that a higher volume ratio of high strength inelastic fiber to the total material volume in the balloon walls would lead to a higher burst pressure for the same wall thickness.
Commercially available low compliance fiber reinforced medical balloons and the processes that produce them may only allow limited flexibility in the placement of the high strength inelastic fibers. For example, a process may result in fibers aligned along the axis of the balloon and fibers wrapped around the circumference. This limited choice of fiber orientation is not always the optimum way to orient the fibers for maximum strength. This limited choice of fiber orientation is not always the optimum way to orient fibers to resist puncture or ripping.
Commercially available low compliance fiber reinforced medical balloons and the processes that produce them may not allow for a large variety of different balloon shapes to be manufactured.